A torsion damper of the above kind is described in the specification of U.S. Pat. No. 4,883,156, in which the housing contains a secondary damper plate surrounding the hub and coupled in rotation to the latter, together with two secondary guide rings which are arranged on either side of the secondary damper plate. Between the secondary guide rings and the secondary damper plate, circumferentially acting resilient means are arranged to act, these resilient means being of lower stiffness than the circumferentially acting resilient means which couple the main damper plate to main guide rings which are themselves coupled together and arranged on either side of the main damper plate. The pre-damper is fitted between one of the main guide rings and the main damper plate.
In the above mentioned United States patent specification, the secondary guide rings are arranged for rotation with the housing of the pre-damper, but are movable axially with respect to the housing, while being retained axially between a first and a second shoulder carried by the housing. The above mentioned coupling means comprise a plurality of coupling fingers carried by the housing, with each coupling finger being arranged to cooperate with a complementary aperture of the main damper plate. The first shoulder carried by the housing (i.e. that one of the said shoulders that is the nearer to the main damper plate) is defined by a plurality of resiliently deformable, hooked tongues which are formed in an axially oriented flange of the housing, these tongues being overlaid by two of the said coupling fingers.
The above arrangement is in many respects satisfactory, since it enables the pre-damper to be fitted easily by simple axial threading of its components into the housing. Nevertheless it increases the axial size of the damper as a whole, since it is necessary that the tongues be positioned back from the free end of the axial flange of the housing so as to avoid any interference with the main damper plate.